1. Field of the Invention
The present invention relates generally to a radio communication system, and more particularly, to a PCD (Personal Communication Device) and a method capable of indicating the transmitted RF power strength level of a radio communication terminal by outputting the power strength level of a transmitter of the radio communication terminal to an indicating device.
2. Description of the Related Art
AMPS, PHS, NADC, GSM, DCS, PCS, IS-95, CDMA, WCDMA, DECT, WLAN (802.11), DECT, CT0, CT1, . . . etc. are well known standards for wireless network and PCDs(personal communication devices). Personal communication devices include cellular phones, cordless phones, PDAs, walkie-talkies, smart phones and others. All personal communication devices mentioned above are wireless communication devices(or radio communication devices). Communication links among PCDs are established through receiving and transmitted radio-frequency signal. The frequency range of these radio frequency covers from VHF to microwave frequency. In order to extend the communication range, PCDs can transmit RF signal up to two Watts.
A personal communication device such as a cellular phone can
A personal communication device such as a cellular phone can be seen generally as depicted in FIG. 1, it consists of a RF(Radio Frequency) receiver Section 14, a RF Transmitter 18, a Frequency Synthesizer 146 186, a Digital/Controller Section 15, a Battery (not shown) and a I/O Section(not shown) etc,.
One example of the PCD as shown in FIG. 1 is a cellular phone handset which complied with the standards above. The handset 1 includes an antenna 11, a LPF(lowpass filter) 12 a receiver(RX) 14, a LPF 16, a transmitter (TX) 18 and a digital/controller 15, wherein the receiver(RX) 14 includes a LNA(low noise amplifier) 142 a mixer 144 and a frequency synthesizer 146. similarly, the transmitter(TX) 18 includes an power amplifier 182, a mixer 124 and a synthesizer 186 an modulator 188.
When a cellular phone handset is used, it is a very common practice for its user to have the handset very close to user's head in order to talk and to listen. The handset radiates RF (Radio Frequency) signal into air to establish communication link to a base station. But, the transmitted RF signal is not only radiated to air but also penetrates into the user's head. Some scientific studies have shown that long-term exposure under the RF signal radiation could damage human tissue. One IEEE paper proposed by M. D. Taurisano etc., having a title of “Measurements of Thermal Effects on a Human Head exposed to 900 MHz” and presented on IEEE MTT Symposium 2000, Boston., presents results of experiments concerning thermal effects due to electromagnetic exposure from handheld mobile communication equipments.
Today, personal communication devices such as cellular phone handsets, cordless phone etc. provide users some information such as RSSI (received signal strength indication) (for example, U.S. Pat. No. 6,356,745 disclose the RSSI), battery low signal and battery charge status etc., but none of them provides TSSI(transmitted signal strength indication) (or called transmitted power indication) to the users for warning the high transmitted power state about their handset.
Also the cellular phone's TSS (transmitted signal strength) is not a constant, how much RF power the cellular phone handset could transmit is subject to the specific regulations and base station instruction. It means the base station will tell the handset how much RF power handset could transmit.
Base station's instruction depends on the communication environmental conditions such as distance, surrounding building and terrain etc. between the cellular phone and the base station. By now, the cellular phone user has no idea how the TSS (transmitted signal strength) of his cellular phone is.
Because scientific studies show that long-term exposure to RF signal can damage human tissues. Therefore there is a need in the prior art to have PCDs that can inform users how much the TSS(transmitted signal strength) is. Thus the PCD users can make some action to reduce the damage to their tissues from such TSS information.